B16 melanoma subpopulations constituting a model system for studying spontaneous metastasis differentially express antigens associated with three cell surface glycoproteins related to murine leukemia virus gp70 (designated B16-gp70, B16-gp80, and B16-gp85). These antigens are the only cell surface antigens that are targets of antibody formation by syngeneic mice immunized with irradiated melanoma cells, and host immunity influences growth and metastasis of viable melanoma inocula. Specific host immunity effects on metastasis, and prospects for specific immunotherapy of tumor metastasis, will be examined using monoclonal antibodies to B16-gp70/80/85 antigens. These antibodies will be produced and used to characterize: (1) antigen molecular organization, by radioimmunoprecipitation, electrophoresis, and tryptic peptide mapping; (2) cell and tissue distribution, by immunofluorescence; and (3) antibody-induced modulation of cell surface antigenicity, whereby cells are rendered resistant to immune destruction, in a radiolabeled Clq binding assay. Passive immunotherapy of metastasis will be assessed by administering monoclonal antibodies to tumor-bearing mice. Affinity chromatography on substrate-bound monoclonal antibodies will be used to purify antigens from cultured cells for administration to mice to elicit active immunity, as a test of active immunotherapy of metastasis. To determine whether host immune responsiveness to B16-gp70/80/85 antigens specifically influences metastasis, host immunity will be made to focus on artificially-introduced antigens in the form of contaminating mycoplasma; mice immunized against mycoplasma will be challenged with mycoplasma-infected B16 melanoma cells. The role of macrophages in nonspecific host immunity to tumor growth and metastasis will also be investigated. Macrophages in tumors and in lung metastases will be enumerated quantitatively, localized in tissues sections by histochemical demonstration of nonspecific esterases or by visualization of uptake of fluoresceinated bacterial polysaccharides, and isolated. Macrophages isolated from normal, immunized, and tumor-bearing mice will be studied for cytostatic or cytolytic effects on cultured melanoma cells, by use of radioisotope-release assays. Normal syngeneic mouse serum stimulates proliferation of low-density monolayer cultures of B16 melanoma cells, and influences of serum factor(s) on tumor cell behavior and on macrophage effects on tumor cells in culture will be investigated. (IB)